Light deflection apparatus

ABSTRACT

Light deflection apparatus for selectively deflecting a beam of light from a source to any one of a plurality of discrete positions on a target is provided. Operative under electro-optic control, the apparatus is of the external reflecting type. A light beam propagated as a set of extraordinary rays never enters the light deflecting birefringent element but is reflected on incidence at it. Astigmatic aberrations in the possible output beams are avoided, pathlength compensation between the two possible output beams of a deflecting stage is achieved, and a diffraction limited spot of light is provided as the output beam.

OR 3,584.93; 9w 5 United States P1 M V :KWEW/ 111 3,534,933

12 Inventor! MllhrdA.Hlbeggr-: 3.449576 6/1969 HOfl'manJr. m1. 350/157 JanesLlpp,botholPoughkeepde,N.Y. 3,481,661 12/1969 Harris 350/150 [2 pp 814,140 OTHER REFERENCES :gg x2323? Harris el al., Digital Laser Beam Deflection," LASER [m Assign" h i In Mum Focus,v6|.3,N6.7 A i.1967),p 26- 32, 350-0102.

Corporation Primary Examiner-David Schonberg Annonk, N.Y. Assistant Examiner- Paul R. Miller Atlorneys- Hanifin and .lancin and John F. Ostemdorf [54] LIGHT DEFLECTION APPARATUS 11 Chile, 9 Drawing Fl US. Cl. deflection apparatus for selectively 350/]47, 350/l52, 350/l57, 350/Dl 2 deflecting a beam of light from a source to any one of a pluh. rality of discrete positions on a target is rovided Operative 350/147- under electro-optic control, the apparatus is of the external 0, i DIG 2 reflecting type. A light beam propagated as a set of extraordinary rays never enters the light deflecting birefringent element [56] Ram Cm but is reflected on incidence at it. Astigmatic aberrations in UNITED STATES PATENTS the possible output beams are avoided, pathlength compensare.26,l7 Q 3/1967 Harris 350/150X tion between the two possible output beams of a deflecting stage is achieved, and a diffraction limited spot of light is pro- 3,391,972 7/1968 Harris et al. 350/150 vided as the output beam.

P'ATENTEUJUNI 5l97| 3.584.933 sum 1 0F 3 c I d INVENTORS m A. HABEGGER JA LIPP BY ATTQRNEY memmumsmn 3534.933 3 sum 2 0r 3 FIG.4

PATENTEDJUNISIQH Y 35 4 9533 sum 3 0r 3 FIG.8

85a as {4 MIRROR MIRR R 88 95 94 a? 0 FIG.9

LIGHT DEFLECTION APPARATUS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to light deflection apparatus and, more particularly, to apparatus employing birefringent deflection elements operative in an external reflection mode under polarization control for deflecting a light beam from a source to a selected location on a target.

2. Description of the PRIOR Art Light deflecting apparatus employing separate birefringent elements and polarization control elements are generally of two types. The first of these is the transmission type. The split angle light deflection apparatus described in application Ser. No. 285,832, now Pat. No. 3,499,700, filed June 5, 1963 in the names of Harris et al. and assigned to the assignee of this invention, is illustrative of the transmission type. Other transmission-type deflectors are those that employ prisms and Wollaston prisms as the birefringent deflection elements.

The second type is the reflection type which operates in either an internal reflection mode or an external reflection mode. An example of the internal reflection type of light deflector is the apparatus described and claimed in US. Pat. No. 3,353,894.

When an image such as that of a character is transmitted through one of the transmission or internal reflection types of deflectors, astigmatic aberrations occur in one of the two possible output beams from each deflecting stage. The astigmatic aberrations produced by the deflecting elements of these deflectors in acting on a convergent beam of light have the efi'ect of rays imaged in the tangential plane focusing at a different location along the system 5 longitudinal axis from the rays imaged in the orthogonal sagittal plane.

The two planes correspond to the planes of incidence on an optical element in which the refractions are extremes in their dissimilarity. The tangential plane coincides in the case of a birefringent element with the plane containing the optic axis and the more or less incident principle ray. The rays contained in the tangential plane form a tangential focal line. Rays in the sagittal plane form a sagittal focal line which is orthogonal to the tangential focal line. The longitudinal distance between these two lines is called the astigmatic difference.

For an image containing rays in both planes the best focus is obtained on a plane located approximately at the midpoint between the sagittal and tangential focal lines. For an ideal point image that has been deflected and incurred astigmatic aberrations, the diameter of this image, which may be defined as the image of least confusion, is determined by the product of the astigmatic difference and the maximum angle between the principle ray and any one of the convergent rays in the light bundle. ln transmission and internal reflection types of light deflectors, astigmatic aberrations are introduced into the focus of the output beam when the beam is projected through the birefringent element as a set of extraordinary rays even when the principle ray is at normal incidence to the face of the plate.

External reflection-type light deflection apparatus is known. Examples of such apparatus are described in application Ser. Nos. 516,367 and 469,068 filed in the names of Harris and Hoffmann et al. respectively, both applications being assigned to the same assignee as this invention. These applications correspond to US. Pat. Nos. 3,48l,661 and 3,449,576, respectively. In the apparatus of these applications astigmatic aberrations are avoided as the extraordinary light rays do not enter and are not transmitted by a birefringent element. However, in the apparatus of both of these applications the possible output beams are not diffraction limited. In the case of the apparatus of application Ser. No. 5 l6,367 (U.S. Pat. No. 3,481,661) the beams from a single stage are of the order of 1 inch apart. In the case of the apparatus of application Ser. No. 469,068 (U.S. Pat. No. 3,449,576) the spacing between the output beams is determined by the thickness of the birefringent elements. This spacing approximates four times the thickness of the birefringent elements. lnherent manufacturing limitations in fabricating the birefringent elements limit the thinness capable of being obtained for these elements. Consequently, it is not possible to provide diffraction limited output spots from this type of deflecting apparatus.

In neither of the deflecting arrangements described in these applications are the deflections of the output spots adjustable, but rather they are fixed. Moreover, in the case of the. apparatus of application Ser. No. 516,367, (U.S. Pat. No. 3,481,661), the output spots are not pathlength compensated but are provided in different focal planes.

SUMMARY OF THE INVENTION As contrasted with the prior art types of light deflection apparatus, light deflectors are described which are free of any astigmatic aberrations. The arrangements of these deflectors are such that the light rays propagated as a set of extraordinary rays do not traverse the birefringent elements but are reflected at their incident faces. The deflections between the possible output beams are adjustable and depend not on the absolute thicknesses of the birefringent elements but on the relative spacings between the incident faces of the birefringent elements and the incident faces of isotropic elements associated with the birefringent elements.

In accordance with one aspect of the invention, a light deflection stage is provided for deflecting a beam of light from a source to either of two possible closely positioned output locations on a target. The apparatus is formed of two pairs of birefringent and isotropic element combinations. The first birefringent element is located at an angle greater than the critical angle for the element with respect to the angle of the principle ray of the incident light beam. An isotropic element is disposed behind the rear face of the birefringent element.

The incident beam encountering the higher index of refraction of this first birefringent element is transmitted through it and is reflected at the incident face of the isotropic element. The beam encountering the lower index of refraction of the birefringent element is reflected at the incident face of the birefringent element and never enters it. The second birefringent plate is positioned in the path of these reflected beams and has its optic axis normal to the optic axis of the first birefringent element. Thus, a beam transmitted through the first birefringent element and reflected at the isotropic element is reflected as an extraordinary beam at the incident face of the second birefringent element. Conversely, the beam reflected at the incident face of the first birefringent element acts as the ordinary beam and passes through the second birefringent element and is reflected at the incident face of the isotropic element associated with the second birefringent element. The outputs are provided in paths substantially parallel to one another and in close proximity to one another. Due to the adjustability of the isotropic plates these outputs may also be provided in nonparallel paths. The outputs are also provided in the same focal plane and are therefore pathlength compensated.

Another aspect of the invention provides for the use of the light deflectors of this invention in an image deflection system. The use of such light deflectors enables the system to deflect images with substantially higher resolution than that obtainable using prior art light deflectors. The resolution for the deflection of characters, graphics and printed circuit configurations employing these deflectors is limited only by the deflectors numeric aperture.

In this system, the deflectors acting on nonimage bearing light beams may be of any type. Those deflectors employed in positioning image bearing light beams utilize only the nonastigmatic deflectors of this invention which provide diffraction limited outputs. The deflection is accomplished in a physically realizable optic aperture by utilizing telescopic lens arrangements for reducing the deflection field between combinations of the light deflectors. The lens arrangements act to control the magnification of the deflection fields to efi'ect passage through the desired aperture and to maintain a constant magnification for the deflection field through the system.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective diagram showing the astigmatic aberration introduced in a convergent light beam by a conventional birefringent element;

FIG. 2 is a diagram showing the magnified diffraction patterns for a convergent light beam propagated as sets of ordinary and extraordinary rays through the element of FIG. 1;

FIG. 3 is a schematic diagram of a light deflecting apparatus according to one aspect of the invention;

FIG. 4 is a schematic diagram of a multistage light deflector of the type shown in FIG. 3;

FIG. 5 is a schematic diagram of a second light deflecting apparatus according to the invention;

FIG. 6 is a detail view showing the mounting and adjusting arrangements for the elements of the light deflector of FIGS. 3 and 5;

FIG. 7 is a schematic diagram of a multistage light deflector of the type shown in FIG. 5;

FIG. 8 is a schematic diagram of an image deflecting system employing the light deflectors of FIGS. 3 and 5; and,

FIG. 9 shows detail views of the effects of the lens arrangements of the system of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT In optical systems, it is usually impossible to secure perfect imagery for even one position of the image of an object transmitted through the optical system. The image shows some defects caused by the aberrations of the system. One such aberration is known as astigmatism. Astigmatism may be defined as a shift in the focal point of the image along the longitudinal axis of the optical system. The object is in fact imaged in two focal planes which are parallel to each other and perpendicular to the principle ray. Between these two image planes the image appears at a location in its most well-defined form. This location has been defined as the image of least confusion.

An astigmatic fonn of aberration occurs when a light beam is transmitted through birefringent material as a set of extraordinary rays. Each ray of the beam has a different angle of incidence on the birefringent material and, therefore, each encounters a different index of refraction. When a light beam is propagated as a set of ordinary rays, all rays are acted on by the same index of refraction.

As shown in FIG. 1, a converging light beam 10 is directed through a birefringent crystal 11 that is formed of a material such as calcite. The optic axis 12 of the crystal is in a plane perpendicular to the incident face of crystal 11. When the light beam 10 has a polarization that is in the horizontal plane, such as the plane 13 corresponding to the same plane as the optic axis 12 of crystal 1], the light beam is propagated as a set of extraordinary rays in crystal 11. A primary image for this light beam occurs at the tangential focal location 14. A secondary image occurs at the sagittal focal location 15. The focal locations l4, present images that are perpendicular to one another. Thus, the image at location 14 is in the vertical plane and the image at location 15 is in the horizontal plane. Located approximately midway between locations 14, 15 is the image of least confusion l6.

As shown in FIG. 2 the diffraction patterns of the images for the beam propagated as a set of extraordinary rays through crystal 11 indicate that the tangential image is a bar of light in FIG. 2a. The sagittal image is orthogonally displaced as a bar of light in FIG. 20. The image of least confusion is indicated in FIG. 2b. The image in FIG. 2b is contrasted with the circular aperture of FIG. 2d corresponding to a convergent light beam directed through birefringent crystal ll of FIG. 1 as a set of ordinary rays. The Airy disc diameter of FIG. 2d for a beam propagated as a set of ordinary rays through a crystal having a thickness approximately 54 mm. has been found to be 24 microns. This image is undistorted whereas the image of least confusion of FiG. 2b suffers from astigmatism. The diameter of this distorted image is approximately four times greater than that of the undistorted image of FIG. 2d. Under the same conditions, this diameter has been found to be approximately microns. It is readily apparent, therefore, that when images of characters are propagated through light deflecting systems the resolution of such systems is severely limited when the image is propagated as a set of extraordinary rays of light.

The light deflector of FIG. 3 avoids any astigmatic aberrations as the light beam is never propagated through a birefringent crystal as a set of extraordinary rays. The light deflector comprises birefringent elements 20, 21 in the form of plates. Each plate has an isotropic element 22, 23 associated in juxtaposed position with respect to it. It is to be understood that the phrase juxtaposed position as used in this application means closely situated in actual contact or spaced in close proximity.

The isotropic element 22 is shown as being a coating applied to the back face of birefringent plate 20. It has an index of refraction that is equal toor less than the lower index of refraction for plate 20.

Isotropic element 23 is a plate whose position with respect to the back face of birefringent plate 21 may be suitably adjusted. It will be apparent from the description which follows hereinafter that plate 23 may also take the form of a coating applied to the back face of birefringent plate 21. Plate 23 similarly has an index of refraction that is equal to or less than the lower index of refraction of the birefringent plate 21.

The optic axes of birefringent plates 20, 21 are disposed in directions normal to one another. Thus, optic axis 24 of plate 20 is in a plane parallel to the incident face of plate 20, whereas optic axis 25 of plate 21 is in a plane perpendicular to the incident face of plate 21. The entire structure is located in a suitable material such as an oil bath having an index of refraction substantially equal to the higher index of refraction of the birefringent plates.

Associated with this deflecting apparatus is a suitable polarization control element which acts to present a light beam having a linear polarization in one of two mutually orthogonal states. The polarization control element may take the form of a potassium dihydrogen phosphate (KDP) crystal having suitable electrodes affixed to the surfaces of it. In one condition, when the KDP crystal is deactivated, the polarization of an incident light beam remains unaffected. When the KDP crystal is activated by applying a voltage between the electrodes that is related to the wavelength of the light, the crystal rotates the polarization state to the mutually orthogonal state. The deflecting stage responds to the polarization of the incident light beam to provide one of two possible output beams.

Thus, a light beam 26 is provided to the deflecting stage at an angle of incidence that is greater than the critical angle a for the particular birefringent crystal 20. When beam 26 has a polarization that is in a plane corresponding to the plane of optic axis 24, that is in a plane perpendicular to the plane of the drawing, it encounters the lower index of refraction of plate 20. Such a beam is reflected at the incident face of plate 20 as beam 27. It follows a path toward birefringent plate 21. Plate 21 is displaced from plate 20 and positioned parallel to it. If the optic axis 25 of plate 21 is in a normal position to optic axis 24 of plate 20, beam 27 encounters the higher index of refraction of plate 21 and passes through it without any refraction. It encounters the incident face of isotropic plate 23 and is reflected as beam 28 in a path substantially parallel to the path of incident beam 26. An output spot is provided at 30 in focal plane 29.

In similar manner, if the polarization of incident beam 26 is in a plane perpendicular to the plane of optic axis 24 of crystal 20, that is, in a plane parallel to the plane of the drawing, it encounters the higher index of refraction of plate 20 and passes through it to isotropic layer 22. At the incident surface of layer 22 the beam is reflected as beam 31 toward birefringent plate 20. Since optic axis 25 of plate 21 is in a normal direction to optic axis 24 of plate 20. beam 31 encounters the lower index of'refraction of plate 21 and is reflected as beam 32 at the incident face of plate 21. To assure that both possible output beams traverse the same pathlengths so that the output spots of light are provided at 30 and 33 in focal plane 29, an optical element 34 is inserted in the path of beam 31. Element 34 is any suitable optical material having an index of refraction higher than the index of refraction of the oil within which the deflection elements are located.

It is readily apparent that with the deflection apparatus of FIG. 3 the light beam propagated as a set of extraordinary rays at the birefringent elements never traverses these elements but is reflected at the incident face of them. Astigmatism in the output beams is thus completely eliminated. It is also apparent that the position between the outputs at 30 and 33 is not dependent on the thicknesses of the birefringent plates 20, 21. The deflection occurring between beams 28 and 32 is determined by the difference in the distances between the incident face of each birefringent element and the incident face of its associated isotropic element. These distances are indicated as h and h, Distances il and h, are not required to be equal.

Isotropic layer 22 is shown as a coating affixed to the rear side of birefringent plate and isotropic plate 23 is shown as being adjustable with respect to the rear face of birefringent plate 21. By suitably adjusting and locking the location of plate 23, such aswill be described in connection with'FlG. 6, the location of the output spots 30 and 33 is controlled. In addition, the angular orientation of isotropic plate 23 can also be adjusted to control the angular relationship between the output spots 30 and 33. As the spacing between these outputs depends on the differences between it, and h it is apparent that the birefringent plate 21 can be made thicker than birefringent plate 20 and isotropic plate 23 formed as a coating on the rear face of plate 21.

For the implementation of the deflection apparatus of FIG. 3, calcite is a suitable birefringent material and sodium fluoride is a suitable low index isotropic material. Utilizing these materials the optic path difference between output beams 28 and 32 for a deflection D is 0.41 D. When optical element 34 is inserted in the path of beam 31 this path difference is eliminated. The calcite birefringent element having an ordinary index of refraction of 1.66 at a wavelength of light 5100 A. is immersed in an oil with an index of refraction of 1.63. It is also possible to achieve the compensation for pathlength difference by forming birefringent plates 20, 21 with suitable difference in thickness.

Only the principle ray is shown in beam 26 as being acted on in the deflecting arrangement of FIG. 3. It is readily apparent that beam 26 may be a collimated beam of light. It may also be a converging beam of light in which the output spots 30, 33 are brought to a focus in focal plane 29.

A plural stage light deflector employing the deflection apparatus of FIG. 3 is indicated in FIG. 4. Two such stages are shown. Each stage includes a polarization control element 40, 41 and a deflecting arrangement generally indicated at 42, 43. A source of linearly polarized light (not shown) such as a laser, provides an incident beam 44 to the deflecting arrangement. Dependent on the polarization state of the beam as controlled by polarization control element 40, beam 44 is either reflected at the incident face of the birefringent element 424 as beam 45 or it is transmitted through birefringent element 424 to the incident face of isotropic plate 42b for reflection as beam 46. Beam 45 encounters the higher index of refraction of birefringent element 42c and is transmitted through it to the incident face of isotropic element 42d for reflection as beam 47. Beam 46 encounters the lower index of refraction of birefringent plate 42c and is reflected at the incident face of this plate as beam 48.

Beams 47, 48 are provided to the second stage of the deflector and the polarization of the beam is acted on by control element 41. The linear polarization state is either rotated to a linear orthogonal state or left unchanged. Beam 47 is incident on birefringent plate 430 encountering the lower index of refraction of this plate. It is reflected at the incident face as beam 49. If the polarization is altered by control element 41 so that the polarization of beam 47 is orthogonal to the optic axis of plate 43a, the higher index of refraction is encountered and the beam is transmitted through plate 43a to encounter isotropic plate 43b. It is reflected at the incident face of plate 431) as beam 50.

In similar manner, if the polarization of beam 48 is not altered by control element 41, it encounters the higher index of refraction of plate 43a and is transmitted through it for reflection as beam 51. If control element 41 rotates the polarization of beam 48 to place it in the orthogonal linear polarization state, it is reflected at the incident face of plate 43a as beam 52. Birefringent plate 43c and isotropic plate 43d act to provide one of four possible output beams 53a-d in focal plane 54.

In like manner, additional stages, each including a polarization control element and a deflection apparatus such as shown in FIG. 3, may be added to increase in binary manner the number of possible output beams. Although the plural stages of the light deflector of FIG. 4 are described as operating in one common coordinate, it is readily apparent that groups of such stages may be arranged with one group orthogonal to the other to provide deflection in two orthogonal coordinates to provide both X and Y deflection control.

Each of the possible output beams is controlled solely by altering the difference between the distances h and h, of each deflection arrangement. Precise deflections are obtainable. The apparatus described is capable of producing zero deflection. Images of fields may also be deflected adjacent to one another.

Referring now to FIG. 5, a slightly different type of deflecting arrangement is shown. The deflecting apparatus includes birefringent plates 60, 61 and isotropic plates 62, 63. Each of the isotropic plates 62, 63 is adjustable angularly and axially with respect to its associated birefringent plate. The combination of birefringent plate 61 and isotropic plate 63 is arranged at an obtuse angle with respect to the combination of birefringent plate 60 and isotropic plate 62. The deflecting arrangement is disposed in an oil solution having an index of refraction substantially equal to the higher index of refraction of the birefringent plates 60, 61. The index of refraction of the isotropic plates 62, 63 is selected to be equal to or lower than the lower index of refraction for the birefringent plates.

In this deflecting arrangement, the deflection that occurs and the position between the possible output spots depends on the distances h, and k These distances are measured from the incident face of the birefringent elements to the incident face of the isotropic plates associated with them. It, is required to be the same as it As both isotropic plates 62, 63 are adjustable with respect to the fixed birefringent plates 60, 61 the relative positions of output beams 68, 69 with respect to one another may be controlled.

As shown in FIG. 6, birefringent plate 60 is fixedly mounted. The associated isotropic plate 62 is mounted on an arm 64 for axial movement with respect to the birefringent plate. A lockscrew 65 is positioned to lock the isotropic plate in a desired location with respect to the birefringent plate. In like manner, angular pivoting is accomplished by moving the isotropic plate with respect to the birefringent plate. Lockscrew 66 is provided to achieve the angular positioning. It is also apparent that the same results can be achieved by fixing the positions of the isotropic elements and having the birefringent plates adjustable.

As in the case of the deflecting apparatus of FIG. 3, the optic axes 55, 56 of birefringent plates 60, 61 are made normal to one another. Thus, optic axis55 of plate 60 is in a plane parallel to the incident plane of the plate 60 and optic axis 56 of plate 61 is in a plane perpendicular to the incident face of plate 61. Dependent on the polarization of incident light beam 67 it is either reflected by birefringent plate 60 at the incident face as beam 57, or it is transmitted by birefringent plate 60 for reflecting at the incident face of isotropic plate 62 as beam 58. Subsequent reflection of beam 57 occurs at the incident face of isotropic plate 63 and subsequent reflection of beam 58 occurs at the incident face of birefringent plate 61. Output beams 68, 69 are provided in focal plane 59.

The deflecting arrangement of FIG. does not depend on the thicknesses of the birefringent plates but only on the distances h, and h,. In forming a deflection system precise deflections are required. When the deflector is employed to position 0,018 inch wide characters along a line and the deflection stage must deflect a block of 32 characters next to itself, this stage must produce a deflection of 057610.002 inch or a gap or overlap in the characters along a line is apparent. When this requirement is translated into thicknesses of plates such as those used in prior art deflectors, accuracies of :0,0005 inches in thickness are required. The plates are also required to have parallel faces. The state of the art in manufacturing techniques for such plates render it practically impossible to fabricate plates having such thicknesses. By forming the deflecting arrangement with adjustable isotropic plates so that the spacings can be accurately determined and locked in place the tolerance requirements are easily achieved. The deflection is adjustable and deflections considerably smaller than heretofore obtainable are accomplished.

A plural stage light deflector employing the deflecting arrangement of FIG. 5 is shown in FIG. 7. Each stage includes a polarization control element 70, 71 and a deflecting arrangement 72, 73 of the type shown in FIG. 5. This arrangement operates in the same manner as the plural stage deflector of FIG. 4.

An incident linearly polarized light beam 74 is acted on by the polarization control element or remains unchanged and is directed to the deflecting arrangement. The first stage deflecting arrangement 72 provides two possible output beams 75, 76. Dependent on the control exercised by polarization control element 71, the second deflecting stage 73 provides one of four possible output beams 77a-d in the same focal plane 78. Additional stages of polarization control elements and deflecting arrangements of the type shown in FIG. 5 may be added to increase in binary manner the number of possible output beams obtainable from the plural stage deflectors. As in the deflector of FIG. 4, only the principle ray is shown as being acted on in the light deflector of FIG. 7. The incident beam 74 may be a collimated beam or it may be a convergent beam.

An image deflection system for selecting a character from a mask and suitably positioning it at a desired location on an output medium is shown in FIG. 8. A laser 80 provides a beam 83 of linearly polarized light. A plural stage light deflector 81 which may be of any prior art deflector type operating in response to polarization control, such as the system described above in application Ser. No. 285,832, selects a character from a character mask 82. The beam of light 83 provided by laser 80 is a collimated beam of light that is deflected parallel to itself in selecting a character from mask 82. If mask 82 is formed as an 8X8 matrix of characters, then deflector 81 is required to have three light deflecting stages for deflecting in the X direction and three light deflecting stages for deflecting in the Y direction. After selection of a character from mask 82 the light beam 83a is in noncollimated form. As a result, conventional light deflectors cannot be employed for positioning the beam of light on output medium 84 without encountering problems of astigmatism.

A second deflecting arrangement 85 acts to collapse the font of characters returning them to a common axis. This deflector is of the type described with respect to FIGS. 3. To accomplish the return of the characters to the common axis four stages of deflection are required. Two of these stages are for deflection in the X direction and two in the Y direction.

The remaining deflecting arrangements 86, 87, 88 position the selected character at a desired location on an output medium 84. This medium may be a display screen or a photosensitive medium for printing. For purposes of this description it is understood to consist of a medium having l28-positions on a line and 64 different lines. The deflection stages in deflector 86 are of the type described with respect to FIG. 3, whereas those in deflectors. 87, 88 are of the type described with respect to FIG. 5.

Deflectors 86-88 are each separated one from another by a pair of telescoping lenses. The lenses relay the image from one deflector to the next. All of the deflecting devices cannot be arranged in serial manner without the intervening lenses because the optical path is long and the divergence angle increases as the length of the optical path increases.

Thus, in an image transmitting system with a half-divergence angle approximating 1, an aperture of 0.54 inch is required in a pathlength of 15 inches. When seven deflecting stages are arranged in serial manner, approximately 15 inches of optical pathlength are required. After four stages of horizontal deflection and three stages of vertical deflection which may be accomplished in deflector 86, a matrix of l6X8 output positions is achieved. As each position consists of a block 0.02 inch wide and 0.03 inch high, an aperture of 0,86 inch wide and 0.78 inch high is required at the entrance to deflector 87. This is a large aperture requirement for a deflecting stage.

To reduce the aperture requirements and to control the magnification of the images transmitted through the system, the lens arrangements are included between the deflecting arrangements. Thus, the first combination of lenses comprised of lenses 90, 91 are positioned such that mask 82 is placed a focal distance f, from lens 90. Lenses 90, 91 are separated by a distance equal to the sum of their focal lengths, or f,+f,, as shown in FIG. 9a. The magnification of this lens combination is therefore f /f In similar manner, deflectors 86, 87 have a lens combination including lenses 92, 93 introduced in the optical transmission path between them. Lens 92 is separated from lens 91 by the sum (f,+j},) of the focal lengths of these lenses and lens 93 is separated from lens 92 by the sum (j+f of the focal lengths of lenses 92, 93. Similarly, deflection devices 87, 88 have lenses 94, located between them. Lens 94 is separated from lens 93 by the sum (f.+f,) of the focal lengths of lenses 93 and 94, and lens 94 is separated from lens 95 by the sum (f,+a06) of the focal lengths of lenses 94, 95.

These lens arrangements relay the deflection field between successive light deflectors. The lenses maintain all light rays at small angles with respect to the optic axis of the system, avoiding unwanted noise in the polarization control elements of the deflectors. The central ray in each image position is parallel to the optic axis of the system and after transmission through the two lenses of each pair it remains parallel.

The character shaped information is transmitted between each group of lenses as collimated light. The second lens of each group brings the character back in focus at a distance corresponding to the focal length of the second lens of the group. Thus, lens 95 brings the character entering it into focus at a distance f from lens 95. By employing these lens arrangements no degradation in image quality is experienced in transmitting the image from the character mask to the output medium 84.

As shown in FIG. 9a, the lens combination permits image magnification to be easily changed. This is the ratio of the focal lengths f lfl. Thus, the character A selected from the I character mask at is reduced in size at 101 after transmission through one lens group. Similarly, as shown in FIG. 9b, the deflection field is also adjustable. If four different characters are provided in the plane 102 with spacings of h, between any two of them, this spacing can be reduced in the plane 103 to h by suitably adjusting the telescopic lens arrangement.

In the deflection system, the image magnification is adjusted so that the deflection field size remains approximately constant throughout transmission in the system. Thus, when the deflection field is doubled the image size is reduced by onehalf. The size of the deflection field physically possible is determined by the resolution which the deflectors are capable of supporting and the tolerable aperture of the deflecting arrangements. By utilizing these telescopic lens arrangements substantially better resolution is achieved in transmitting characters, graphics and printed circuit configurations.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What we claim is:

1. ln light deflecting apparatus in which a linearly polarized light beam is provided by source means in either one of two mutually orthogonal states for selective deflection in astigmatic aberration free form to one of two relatively adjustable locations in a common focal plane, the improvement comprising first deflecting means disposed in the path of the incident light beam for deflecting the incident light beam into a first or a second optical transmission path dependent on the polarization state of the beams, said first path'being totally external of the first deflecting means, and

second deflecting means positioned in both said first and second transmission paths for providing a redeflected output at one of said selected locations in the common focal plane dependent on the polarization state of the incident beam, each of said first and second deflecting means comprising birefringent means having an incident face and another face and isotropic means in juxtaposed position with the other face of the birefringent means,

the birefringent means of the first deflecting means being disposed to encounter the incident light beam for deflecting a beam at its incident face into said first path when the beam has one of said mutually orthogonal polarization states and for transmitting a beam to the juxtaposed isotropic means for deflection into said second path when the beam has the other of said mutually orthogonal polarization states,

the birefringent means of the second deflecting means being arranged in both of the first and second paths for transmitting the beam in the first path for redeflection by the juxtaposed isotropic means to one of said selected locations and for redeflecting the beam in the second path at its incident face to the other of said selected locations,

the birefringent means and isotropic means of at least one of said deflecting means being relatively adjustable with respect to one another,

whereby deflection occurs to one of said two relatively adjustable locations in the common focal plane.

. 2. in the apparatus of claim 1, wherein one of said isotropic means is movably adjustable with respect to the juxtaposed birefringent means and the spacing between said adjustable locations is determined by the difference between the distances of the incident faces of birefringent means and the respective juxtaposed isotropic means, said spacing being limited only by the diffraction of said beams provided to said locations.

3. In the apparatus of claim 2, and further comprising optical means disposed in said second path for compensating for pathlength differences traversed by the two beams to said selected locations.

4. In the apparatus of claim 1, wherein both of said isotropic means are adjustable with respect to the respective juxtaposed birefringent means so that the distance between the incident face of both of the birefringent means and the respective juxtaposed isotropic means are substantially equal and the spacing between said adjustable locations is determined by said distance.

5. A light deflection system for interposition between a source of a beam of linearly polarized light and a target to deflect selectively the beam to a location in a common focal plane on the target, comprising a plurality of optically aligned cascaded beam deflecting stages, each stage comprising in the order of the incoming beam of light, means for rotating the state of polarization of the incident beam into one of two mutually orthogonal states, first deflecting means for deflecting the beam provided by the rotating means into a first or second optical transmission path dependent on the polarization state of the beam, said first path being totally external of the first deflecting means, and second deflecting means positioned in both said first and second transmission paths for redeflecting a beam provided in either transmission path so that the redeflected beams are provided in a common focal plane, each of said first and second deflecting means of each of said deflecting stages comprising birefringent means having an incident face and another face and isotropic means in juxtaposed position with the other face of the birefringent means,

the birefringent means of the first deflecting means being disposed to encounter first the incident light beam from the polarization rotation means of that stage for deflecting a beam at its incident face into said first path when the beam has one of said mutually orthogonal polarization states and for transmitting a beam to the juxtaposed isotropic means for deflection into said second path when the beam has the other of said mutually orthogonal polarization states,

the birefringent means of the second deflecting means being arranged in both of the first and second paths for transmitting the beam in the first path for redeflection by the juxtaposed isotropic means to said common focal plane and for redeflecting the beam in the second path at its incident face to said common focal plane,

the birefringent means and isotropic means of at least one of said deflecting means being relatively adjustable with respect to the other,

whereby deflection occurs to one of a plurality of relatively adjustable locations in the common focal plane.

6. The system of claim 5, wherein a first plurality of said stages include first and second deflecting means having orientations providing deflections along a first common coordinate, and a second plurality of said stages include first and second deflecting means having orientations providing deflections along a second common coordinate orthogonal to the first coordinate.

7. The system of claim 5, wherein one of said isotropic means is adjustable with respect to the juxtaposed birefringent means and the spacing between the output beams in the common plane from each stage is determined by the difference between the distances of the incident faces of the birefringent means and the respective juxtaposed isotropic means, said spacing being limited only by the diffraction of said beams.

8. The system of claim 7, and further comprising optical means disposed in the second path of each stage for compensating for pathlength differences traversed by the two beams to the common plane at the output of said stage.

9. The system of claim 5, wherein both of said isotropic means are adjustable with respect to the respective juxtaposed birefringent means of each stage so that the distance between the incident face of both of the birefringent means and the respective juxtaposed isotropic means of each stage are substantially equal and the spacing between the output beams in the common plane is determined by said distance.

10. A high resolution character projection system for projecting in astigmatic aberration free form a beam of linearly polarized light in the form of a desired character from a font of characters laterally spaced from each other to a desired location on a target comprising g a first light deflection means optically aligned with said font of characters for collapsing the font to a predetermined defined aperture on a common axis in anastigmatic form,

a second light deflection means optically aligned with said first deflection means for deflecting the desired character within the defined aperture to position the character at the desired location in anastigmatic fonn,

each of said deflection means being fonned of plural light deflection stages, each stage being adjustable at least in part for controlling the relative output positioning of the possible beams deflected by that stage, and

telescopic lens means disposed at least between said first and second deflecting means for relaying the fleld of the 

1. In light deflecting apparatus in which a linearly polarized light beam is provided by source means in either one of two mutually orthogonal states for selective deflection in astigmatic aberration free form to one of two relatively adjustable locations in a common focal plane, the improvement comprising first deflecting means disposed in the path of the incident light beam for deflecting the incident light beam into a first or a second optical transmission path dependent on the polarization state of the beams, said first path being totally external of the first deflecting means, and second deflecting means positioned in both said first and second transmission paths for providing a redeflected output at one of said selected locations in the common focal plane dependent on the polarization state of the incident beam, each of said first and second deflecting means comprising birefringent means having an incident face and another face and isotropic means in juxtaposed position with the other face of the birefringent means, the birefringent means of the first deflecting means being disposed to encounter the incident light beam for deflecting a beam at its incident face into said first path when the beam has one of said mutually orthogonal polarization states and for transmitting a beam to the juxtaposed isotropic means for deflection into said second path when the beam has the other of said mutually orthogonal polarization states, the birefringent means of the second deflecting means being arranged in both of the first and second paths for transmitting the beam in the first path for redeflection by the juxtaposed isotropic means to one of said selected locations and for redeflecting the beam in the second path at its incident face to the other of said selected locations, the birefringent means and isotropic means of at least one of said deflecting means being relatively adjustable with respect to one another, whereby deflection occurs to one of said two relatively adjustable locations in the common focal plane.
 2. In the apparatus of claim 1, wherein one of said isotropic means is movably adjustable with respect to the juxtaposed birefringent means and the spacing between said adjustable locations is determined by the difference between the distances of the incident faces of birefringent means and the respective juxtaposed isotropic means, said spacing being limited only by the diffraction of said beams provided to said locations.
 3. In the apparatus of claim 2, and further comprising optical means disposed in said second path for compensating for pathlength differences traversed by the two beams to said selected locations.
 4. In the apparatus of claim 1, wherein both of said isotropic means are adjustable with respect to the respective juxtaposed birefringent means so that the distance between the incident face of both of the birefringent means and the respective juxtaposed isotropic means are substantially equal and the spacing between said adjustable locations is determined by said distance.
 5. A light deflection system for interposition between a source of a beam of lineArly polarized light and a target to deflect selectively the beam to a location in a common focal plane on the target, comprising a plurality of optically aligned cascaded beam deflecting stages, each stage comprising in the order of the incoming beam of light, means for rotating the state of polarization of the incident beam into one of two mutually orthogonal states, first deflecting means for deflecting the beam provided by the rotating means into a first or second optical transmission path dependent on the polarization state of the beam, said first path being totally external of the first deflecting means, and second deflecting means positioned in both said first and second transmission paths for redeflecting a beam provided in either transmission path so that the redeflected beams are provided in a common focal plane, each of said first and second deflecting means of each of said deflecting stages comprising birefringent means having an incident face and another face and isotropic means in juxtaposed position with the other face of the birefringent means, the birefringent means of the first deflecting means being disposed to encounter first the incident light beam from the polarization rotation means of that stage for deflecting a beam at its incident face into said first path when the beam has one of said mutually orthogonal polarization states and for transmitting a beam to the juxtaposed isotropic means for deflection into said second path when the beam has the other of said mutually orthogonal polarization states, the birefringent means of the second deflecting means being arranged in both of the first and second paths for transmitting the beam in the first path for redeflection by the juxtaposed isotropic means to said common focal plane and for redeflecting the beam in the second path at its incident face to said common focal plane, the birefringent means and isotropic means of at least one of said deflecting means being relatively adjustable with respect to the other, whereby deflection occurs to one of a plurality of relatively adjustable locations in the common focal plane.
 6. The system of claim 5, wherein a first plurality of said stages include first and second deflecting means having orientations providing deflections along a first common coordinate, and a second plurality of said stages include first and second deflecting means having orientations providing deflections along a second common coordinate orthogonal to the first coordinate.
 7. The system of claim 5, wherein one of said isotropic means is adjustable with respect to the juxtaposed birefringent means and the spacing between the output beams in the common plane from each stage is determined by the difference between the distances of the incident faces of the birefringent means and the respective juxtaposed isotropic means, said spacing being limited only by the diffraction of said beams.
 8. The system of claim 7, and further comprising optical means disposed in the second path of each stage for compensating for pathlength differences traversed by the two beams to the common plane at the output of said stage.
 9. The system of claim 5, wherein both of said isotropic means are adjustable with respect to the respective juxtaposed birefringent means of each stage so that the distance between the incident face of both of the birefringent means and the respective juxtaposed isotropic means of each stage are substantially equal and the spacing between the output beams in the common plane is determined by said distance.
 10. A high resolution character projection system for projecting in astigmatic aberration free form a beam of linearly polarized light in the form of a desired character from a font of characters laterally spaced from each other to a desired location on a target comprising a first light deflection means optically aligned with said font of characters for collapsing the font to a predetermined defined aperture on a cOmmon axis in anastigmatic form, a second light deflection means optically aligned with said first deflection means for deflecting the desired character within the defined aperture to position the character at the desired location in anastigmatic form, each of said deflection means being formed of plural light deflection stages, each stage being adjustable at least in part for controlling the relative output positioning of the possible beams deflected by that stage, and telescopic lens means disposed at least between said first and second deflecting means for relaying the field of the projected character between successive light deflection means with a predetermined magnification so that said projected character is within said defined aperture.
 11. The system of claim 10, wherein each of said light deflection stages is pathlength compensated and said lens means are arranged as pairs of telescoping lenses between groups of said stages, so that the images of said characters are provided at said target free of image degradation. 